What all controls what sleep modes are available? Just the BIOS? Or does the HDD also have a role in what sleep modes are offered in the BIOS?

I have a Lenovo M58P SFF model and the only sleep mode I have is S3 in my BIOS. No other modes are offered which is odd? I have ran powercfg only to see the same S3 sleep state supported. Id like to have S1 or S2 also available, but im not sure if this is possible.. Anyone know much about sleep modes? Thanks in advance!

I know enough about sleep modes to tell you that you don't need S1 and S2. Nobody uses them and I don't think they are actually support on most systems in the past ~10 years.

Sleep modes in general are very tricky and depend on a lot of factors - BIOS, OS and drivers. But if you get S3 (standby) and S4 (hibernate) supported - that is probably all you will you ever get or need on a system such as the M58p.